Like others said, same but different.
Alot probably depends on the area you are diving. For me, there was a lot more going on for our first open water dives, so there is a lot more sensory input than in the pool. That took a little getting used to (like everything when new, it takes a while to cope with all the new sensory input).
For us (wife and I) it was also cold as &*&! when we did our O/W dives (57* here in DFW), so that was a definite distraction.
As far as speed, it's the same, but you'll have a more open area, so something to look at and swim toward. You may not end up doing a whole lot of swimming though, mostly drills.
Buoyancy is easier to control a little deeper once your suit "crushes" (if wearing a wetsuit), but in O/W you'll be more mindful of touching bottom - in the pool it's alot easier to just put a foot down and not realize/care...
Have FUN!!!!